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On December 28, 2002, at 0440 hours, a low … On December 28, 2002, at 0440 hours, a low voltage condition was discovered on Modular Power Unit (MPU) 3, Distribution Cabinet 2. Investigation into this condition concluded that the 120 VAC voltage regulator associated with MPU 3 had degraded such that the output voltage was 93 VAC. MPU 3 is a non-Class lE 120 VAC Instrumentation and Control Power (ICP) System that provides related Balance of Plant (BOP) instrumentation and control loads including several control circuits, indicators and recorders in the control room. It was concluded that a loss of the feedwater pumps and the circulating water pumps could occur if operation were allowed to continue, or if on line repair was attempted.</br></br>Reactor power was reduced to approximately 73 percent using recirculation flow. Further power reduction using control rods was then attempted when it was found that control rods could not be moved using the Reactor Manual Control System (RMCS). The inability to manually move rods during the power reduction was attributed to the degraded voltage on MPU 3. The normal power reduction was stopped and the reactor was manually scrammed on December 29, 2002, at 0010 hours.</br></br>All other systems responded as expected. Following shutdown, the voltage regulator in MPU 3 was bypassed under a temporary modification to allow an upstream voltage regulator associated with its normal power supply, Bus 72 F, to control the MPU 3 voltage.y, Bus 72 F, to control the MPU 3 voltage. +
On December 28, 2002, at 0440 hours, a low … On December 28, 2002, at 0440 hours, a low voltage condition was discovered on Modular Power Unit (MPU) 3, Distribution Cabinet 2. Investigation into this condition concluded that the 120 VAC voltage regulator associated with MPU 3 had degraded such that the output voltage was 93 VAC. MPU 3 is a non-Class lE 120 VAC Instrumentation and Control Power (ICP) System that provides related Balance of Plant (BOP) instrumentation and control loads including several control circuits, indicators and recorders in the control room. It was concluded that a loss of the feedwater pumps and the circulating water pumps could occur if operation were allowed to continue, or if on line repair was attempted.</br></br>Reactor power was reduced to approximately 73 percent using recirculation flow. Further power reduction using control rods was then attempted when it was found that control rods could not be moved using the Reactor Manual Control System (RMCS). The inability to manually move rods during the power reduction was attributed to the degraded voltage on MPU 3. The normal power reduction was stopped and the reactor was manually scrammed on December 29, 2002, at 0010 hours.</br></br>All other systems responded as expected. Following shutdown, the voltage regulator in MPU 3 was bypassed under a temporary modification to allow an upstream voltage regulator associated with its normal power supply, Bus 72 F, to control the MPU 3 voltage.y, Bus 72 F, to control the MPU 3 voltage. +
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